1. Field of the Invention
The invention pertains to the field of contact sensors. More particularly, the invention pertains to a self-aligning apparatus for a contact sensor.
2. Description of Related Art
Ultrasonic pulse-echo testing of materials requires an ultrasonic transducer to introduce an ultrasonic stimulus wave into a test material, and for reflected ultrasonic waves to be detected and analyzed. The ultrasonic stimulus waves can be either compression or shear waves. It is common for a single ultrasonic transducer to be used to both introduce the stimulus wave and to detect reflected waves. To ensure that the stimulus wave is introduced into the test material by the transducer, and that reflected waves are conducted back to the transducer, the transducer face must be placed into good physical contact with the surface of the test material. In cases where the curvature of the test material surface is not known a priori, it is common for general purpose ultrasonic transducers to possess a flat front surface.
When a general-purpose ultrasonic transducer with a flat front surface is positioned by a skilled human operator, the operator places the transducer against a test material surface and applies pressure to push the transducer's front surface against the test material surface. The operator then adjusts the transducer alignment until proper acoustic coupling between the transducer face and the test material surface is obtained. Such manual placement of a contact transducer works, because the trained operator uses skill derived from past experience in order to adjust the transducer position. In some applications, a coupling fluid, which is conventionally water, is used between the end of the transducer and the test material surface. Transducer placement by unskilled operators or by mechanical or automated mechanisms such as robots results in less reliable transducer positioning, especially on test materials with curved surfaces, because the front surface of the transducer does not automatically align to the surface of the test material. To enable reliable and repeatable ultrasonic measurements with contact transducers, it is important that the transducer alignment process be fast and repeatable, even when the transducer is placed by an unskilled operator or by a robot.